1538-A Strobotac Electronic Stroboscope

♦ PRECISION INSTRUMENTS FOR TEST AND MEASUREMENT ♦

User and Service Manual

1538-A im/March, 2002 IET LABS, INC. Standards • Decades • Strobes • Sound Level Meters • Bridges Formerly manufactured by 534 Main Street, Westbury, NY 11590 TEL: (516) 334-5959 • (800) 899-8438 • FAX: (516) 334-5988 GenRad www.ietlabs.com

WARRANTY

We warrant that this product is free from defects in material and workmanship and, when properly used, will perform in accordance with applicable IET specifications. If within one year after original shipment, it is found not to meet this standard, it will be repaired or, at the option of IET, replaced at no charge when returned to IET. Changes in this product not approved by IET or application of voltages or currents greater than those allowed by the specifications shall void this warranty. IET shall not be liable for any indirect, special, or consequential damages, even if notice has been given to the possibility of such damages.

THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, INCLUD- ING BUT NOT LIMITED TO, ANY IMPLIED WARRANTY OF MERCHANTIBILITY OR FITNESS FOR ANY PARTICULAR PURPOSE.

WARNING

OBSERVE ALL SAFETY RULES WHEN WORKING WITH HIGH VOLTAGES OR LINE VOLTAGES.

Dangerous voltages may be present inside this instrument. Do not open the case Refer servicing to qulified personnel

HIGH VOLTAGES MAY BE PRESENT AT THE TERMINALS OF THIS INSTRUMENT

WHENEVER HAZARDOUS VOLTAGES (> 45 V) ARE USED, TAKE ALL MEASURES TO AVOID ACCIDENTAL CONTACT WITH ANY LIVE COMPONENTS.

USE MAXIMUM INSULATION AND MINIMIZE THE USE OF BARE CONDUCTORS WHEN USING THIS INSTRUMENT.

Use extreme caution when working with bare conductors or bus bars.

WHEN WORKING WITH HIGH VOLTAGES, POST WARNING SIGNS AND KEEP UNREQUIRED PERSONNEL SAFELY AWAY.

CAUTION

DO NOT APPLY ANY VOLTAGES OR CURRENTS TO THE TERMINALS OF THIS INSTRUMENT IN EXCESS OF THE MAXIMUM LIMITS INDICATED ON THE FRONT PANEL OR THE OPERATING GUIDE LABEL. Contents

Section 1 INTRODUCTION ...... 1 1. General Description of a Stroboscope ...... 1 1.1. What it is ...... 1 1.2 How it works...... 1 1.3 The Type 1538 Strobotac® Electronic Stroboscope ...... 2 1.3.1 General Description ...... 2 1.3.2 Controls and Connectors ...... 2 1.3.3 Accessories Supplied ...... 4 1.3.4 Accessories Available ...... 4 Section 2 OPERATING PROCEDURE ...... 6 2.1 Opening the Case ...... 6 2.2 Closing the Case ...... 6 2.3 Power Requirements...... 6 2.3.1 Power-Line Operation ...... 6 2.3.2 Battery Operation ...... 7 2.3.3 Type 1538-P3 A Battery Source and Charger ...... 7 2.4 Turning the Instrument On ...... 8 2.5 Positioning the Stroboscope ...... 8 2.6 Adjusting the Flashing Rate ...... 8 2.7 Calibration ...... 8 2.8 Speed Measurements ...... 9 2.8.1 Fundamental-Speed Measurement ...... 9 2.8.2 Submultiple Speed Measurements ...... 10 2.8.3 Measurement of Speeds above 150,000 RPM ...... 10 2.8.4 Low-Speed Operation ...... 11 2.8.5 Slow-Motion Studies ...... 11 2.9 Type 1538-P2 Extension Lamp ...... 11 2.10 External Synchronization ...... 12 2.10.1 Use of the Input Jack ...... 12 2.10.2 Type 1531-P2 Flash Delay and type 1536 Photoelectric Pick-off ...... 12 2.10.3 Type 1537 Photoelectric Pick-off ...... 13 2.10.4 Type 1539 Stroboslave ...... 13 2.10.5 Use of Multiples Stroboscopes...... 13 2.10.6 Connecting the Accessory Instruments ...... 13 2.11 High-Speed Photography ...... 14 2.11.1 General ...... 14 2.11.2 Flash Duration ...... 14 2.11.3 Beam ...... 14 2.11.4 Spectral Characteristics ...... 14 2.11.5 Exposure Data ...... 15 2.11.6 Single-Flash Photography ...... 15 2.11.7 Type 1538-P4 High-Intensity-Flash Capacitor ...... 15 Section 3 PRINCIPLES OF OPERATION ...... 17 3.1 General ...... 17 3.2 The Strobotron Tube ...... 17 3.3 The Charging Circuit ...... 17 3.4 The Calibration Circuit ...... 19 Section 4 SERVICE AND MAINTENANCE ...... 20 4.1 Customer Service ...... 20 4.2 Instrument Return ...... 20 4.3 Minimum Performance Standards ...... 20 4.3.1 General ...... 20 4.3.2 Equipment Required ...... 20 4.3.3 Preliminary Check...... 20 4.3.4 Flashing-Rate Accuracy Check ...... 21 4.3.5 Input Check ...... 21 4.3.6 Output Check ...... 21 4.4 Maintenance ...... 21 4.4.1 Case Will Not Lock Properly ...... 21 4.4.2 Cleaning the Reflector ...... 21 4.4.3 Removing the Instrument from its Case ...... 21 4.4.4 Replacing the Fuse ...... 21 4.4.5 Replacing the Strobotron Lamp ...... 21 4.4.7 Repositioning the RPM Dial and Knob ...... 22 4.4.8 Converting to the other Power-Line Voltage ...... 22 4.5 Trouble Analysis ...... 23 4.5.1 Strobotron Lamp does not Flash ...... 23 4.5.2 Strobotron Lamp Flashes Erratically ...... 24 4.5.3 Improper Operation with External Input ...... 25 4.5.4 Improper Operation with Battery Power ...... 25 4.5.5 Type 1538-P2 External Lamp does not Flash; Front-Panel Strobotron Lamp Flashes ...... 25 4.6 Replacement of Mechanical Parts ...... 26 4.6.1 General ...... 26 4.6.2 Reflector and Cover...... 26 4.6.3 Swivel-Support Assembly, Pivot Blocks, and Washers ...... 26 4.6.4 Scale Mask Assembly ...... 27 4.6.5 Dial ...... 27 Type 1538-P4 High-Intensity-Flash Capacitor (See Figure 2-14) ...... 33 Type 1538-P2 Extension Lamp...... 33 Figures

Figure 1-1. The stroboscope can be mounted on a standard camera tripod...... 2 Figure 1-2. The front panel of the stroboscope, showing the controls and connectors...... 2 Figure 1-3. The Type 1538, powered by the Type 1538-P3 Battery pack, offers a precise bright stroboscope capability completely independent of the ac power line. A unique advantage in use with large machine complexes such as found in textile and printing industries. The battery pack can power the Strobo for up to 8 hours of intermittent use...... 5 Figure 2-1 The transformer terminals on the stroboscope are numbered as shown...... 7 Figure 2-2. Typical charge- retention characteristics of the battery...... 8 Figure 2-3. Stroboscopic images produced by a rotating gear...... 10 Figure 2-4. Type 1538-P2 Extension Lamp...... 12 Figure 2-5. A widely used combination consists of the stroboscope with the Type 1531-P2 Flash Delay and the Type 1536 Photoelectric Pick-off...... 13 Figure 2-6. Some of the many possible combinations of the Type 1538 Strobotac electronic Stroboscope and its accessory instruments...... 13 Figure 2-8. Spectral distribution of the Strobotron’s light output...... 14 Figure 2-7. Plot of light intensity vs time of the Type 1538 Stroboscope...... 14 Figure 2-10. The Type 1538-P4 High-Intensity-Flash Capacitor can be used with the Strobotac for short, single flashes...... 15 Figure 2-11. Circuit of type 1538-P4 High-Intensity-Flash Capacitor...... 16 Figure 3-1. Voltage-vs-time characteristics of various charging circuits...... 18 Figure 3-2. Charging circuit of the Type 1538 Strobotac electronic stroboscope...... 18 Figure 3-3. Block diagram of the Type 1538 Strobotac electronic stroboscope...... 18 Figure 3-4. The voltage buildup on the charging capacitor is in small steps...... 19 Figure 4-1. The power-supply etched-circuit board is pivoted to swing out when screws A and B are removed...... 22 Figure 4-2. The power-supply board swung out to expose the under side, the fuse, and the dial lamp...... 22 Figure 4-3. Right-side interior view of the Stroboscope...... 23 Figure 4-4. Voltage waveform at the panel OUTPUT jack (24,000 RPM)...... 24 Figure 4-5. Voltage waveform at A.T.65 (24,000 RPM)...... 24 Figure 4-6. Voltage waveform at pin # 3 of the panel EXT LAMP socket, S0901 (24,000 RPM)...... 25 Figure 4-7. Voltage waveform at A.T.23 (24,000 RPM)...... 25 Figure 4-8. Voltage waveform at A.T.63 (24,000 RPM)...... 25 Figure 4-9. Miscellaneous part numbers...... 26 Figure 4-10. Interior view showing mounting of the swivel-support assembly, pivot blocks, and connections. . 26 Figure 4-11. Name and location of parts included in the IET Flip-Tilt Case (refer to table 4-1)...... 27 Figure 4-12. Power supply etched-board assembly. (Complete assembly is P/N 1538-2751)...... 28 Figure 4-13. Oscillator etched-board assembly. (Complete assembly in P/N 1538-2710.) ...... 28 Figure 4-14. Switch-circuit etched-board assembly. (Complete assembly is P/N 1538-2721.) ...... 28

Some of the many accessory instruments available for use with the stroboscopes...... 33 Appendix

Type 1539-A Stroboslave and Specifications ...... 34 Type 1531-P2 Flash Delay and Specifications...... 34 Type 1536-A Photoelectric Pickoff and Specifications ...... 35 Type 1537-A - Photoelectric Pickoff and Specifications ...... 35

1538-A Strobotac

Section 1 INTRODUCTION

NOTE The IET Handbook of Stroboscopy describes in detail many stroboscopic techniques and applications. 1. General Description of a Stroboscope The following example illustrates this principle: A white disc, with a single black dot, is mounted on the shaft of a 1200-rpm motor. 1.1. What it is When the disc is rotating at 1200 rpm, A stroboscope is a source of flashing light that can be it is impossible for the human eye to synchronized with any fast, repeating motion so that distinguish a single image and the dot a rapidly moving device seems to stand still, or to move appears to be a blurred continuous slowly. circle. When the disc is illuminated by the 1.2 How it works flashing Strobotac® light, which is synchronized to flash once every revolu- To understand how the stroboscope stops or slows tion of the disc (when the dot is at 3 down motion, consider a fan rotating at 1800 revolu- o’clock, for example), the dot will be tions per minute, and a light that is switched on and seen at this position - and only at this off 1800 times a minute (i.e., a stroboscope). Since position - at a rate of 1200 times each the time between flashes is the time it takes the fan minute. Thus, the dot will appear to to make one revolution, every time the light flashes, ”freeze” or stand still. the fan blades are exactly where they were the previous time. The blades are never seen in any other Now, if the flashing rate of the strobo- position; thus it appears that the fan isn’t moving at scope is slowed to 1199 flashes per all. (The retina of the eye holds one image until the minute, the dot will be illuminated at a next flash, so there is little, if any, flicker.) If the light slightly different position each time the is switched on and off 1801 times a minute (with the disc revolves, and the dot will appear fan still turning at 1800 rpm), it is flashing faster than to move slowly in the direction of ro- the fan is turning. Therefore, each time the light comes tation, through 360° and arrive back at on, the fan blades have not quite reached the position its original position (3 O’clock) one they were in the previous time the light was on. The minute later. fan is seen at progressively earlier parts of its cycle and therefore it appears to be turning very slowly back- A similar movement, but in a direction ward. In like manner, if the light flashes 1799 times a opposite to the rotation of the dot, will minute, it shows the fan blade at successively later be observed if the flashing rate of the parts of its cycle, so that the fan appears to be mov- stroboscope is increased to 1201 rpm. ing very slowly forward. If desired, the rate of apparent movement of the dot can be speeded up by further increasing or decreasing the stroboscope flashing rate.

INTRODUCTION 1 1538-A Strobotac

If the flashing rate of the stroboscope is known, this The flashes of a neon light on the panel serve as an is also the speed of a moving device made to “stop” indicator for calibration. under the stroboscope’s light. Thus, the stroboscope has the dual purpose of measuring speed and of apparently slowing down or stopping rapid motion, for observation. The practical significance of the slow- motion effect is that, since it is a true copy of the high-speed motion, all irregularities (vibration, torsion, chatter, whip present in the high-speed motion can be viewed and studied (refer to paragraph 2.8.5).

1.3 The Type 1538 Strobotac® Electronic Stroboscope Figure 1-1. The stroboscope can be mounted on a standard camera tripod.

1.3.1 General Description The strobotron lamp is mounted on a swivel arm and the reflector can be rotated about the lamp, which Supplementing the basic Type 1531 Strobotac® elec- makes it possible to aim the light beam in almost any tronic stroboscope is the Type 1538 (Figure 1-1). In direction. The high-intensity lamp provides adequate addition to providing a much higher flashing rate than illumination for most objects, even in normal ambient its predecessor, the Type 1538 can be operated from light. an accessory battery pack or from the power line. It When not in use, the detachable ac power cable is can be used with the Type 1538-P2 Extension Lamp wound around the reflector and the range-switch knob to illuminate hard-to-reach areas. With the plug-in (refer to paragraph 2.2). High-Intensity-Flash Capacitor Type 1538-P4, very short flashes of light of 44 million beam candles can 1.3.2 Controls and Connectors be produced for single-flash photography applications. The Type 1538 is a small, portable stroboscope, housed in a General Radio flip-tilt case. This case serves as All controls and connectors are located on the front a tilting base when the stroboscope is in use and pro- panel of the instrument (see Figure 1-3). The type tects the instrument during storage and in transit. The and function of each are given in Table 1-1. cover of the case is permanently attached to the instrument, and the base contains a tripod mounting socket. The stroboscope can be held in the hand, placed on a convenient flat surface, or mounted on a tripod as in Figure 1-1. In the stroboscope, the flashing rate of the tube is governed by the frequency of an internal generator, which is adjusted by means of the RPM controls, a bar knob, and a large-diameter dial. The knob selects any of four direct-reading RPM ranges; the dial is concentric with the bar knob and provides precise setting of the flashing rate. The screwdriver-adjust potentiometers on the panel are used to set the calibration at the low and high ends of the dial. Figure 1-2. The front panel of the stroboscope, showing the controls and connectors.

2 INTRODUCTION 1538-A Strobotac

Table 1-1 Controls, Connectors, and Indicators Figure 1-3 Reference Name Type Function 1 None Reflector Can be rotated to aim the light and swivel beam. arm of Strobotron lamp assembly. 2 EXT LAMP 4-prong Provides a panel connection for socket the Type 1538-P2 Extension Lamp or the Type 1538-P4 High-Intensity Flash Capacitor. 3 115 V 50-60 Hz 4-prong Accepts the power cable from the 24 VDC plug power line or from the Type 1538- P3 Battery and Charger. 4 POWER 2-position Turns instrument ON or OFF. (ON-OFF) toggle switch 5 RPM range switch 5-position Selects any of the four RPM rotary switch ranges or the CAL range. 6 LOW CAL Screwdriver Calibrates the low end of control the RPM dial. through panel 7 RPM dial 4-inch dial Sets the frequency of the in- with fluted ternal oscillator. It is cali- rim brated directly in revolutions per minute. 8 HIGH CAL Screwdriver Calibrates the high end of control the RPM dial. through panel 10 FLASH CONTROL 2-position Selects a signal from either (EXTERNAL- toggle switch the internal generator or one INTERNAL) applied externally at the IN- PUT jack. 11 CALIBRATE Neon lamp Its flashing indicates the correct setting of the CAL potentiometers for calibration of the RPM dial. 12 INPUT Phone jack Connects the stroboscope to an external synchronizing signal from either an electrical device or a mechanical contactor (refer to paragraph 2.10.1). 13 OUTPUT Phone jack Trigger pulse is available at this jack for triggering accessory instruments (refer to paragraph 2.10.8). 14 None 1/2-inch pin Serves as a holding device for (3/16-inch the ac power-cable plug when diameter) the instrument is not in use (refer to paragraph 2.2).

INTRODUCTION 3 1538-A Strobotac

1.3.3 Accessories Supplied 1.3.4 Accessories Available

Supplied with the stroboscope are: The accessories listed in Table 1-2 are available for 4270-1100 - Phone plug for INPUT or OUTPUT jack use with the stroboscope. They are described else- 1538-0420- Ac power cable where in this book, as noted in the table. Figure 1-4 shows a typical setup, using the stroboscope with the pick-off, the flash delay, and the Stroboslave.

-Table 1.2- Available Accessories for the Type 1538 Stroboscope

Type No. Name Function 1538-P3 Battery and Charger Offers rechargeable 24-Volt dc battery- power option (paragraph 2.3.3).

1538-P2 Extension Lamp Operates up to 6 feet from stroboscope (paragraph 2.9). Longer cords available on special order.

1531-P2 Flash Delay Provides continuously adjustable time delay between external trigger pulse and stroboscope flash (paragraph 2.10.2).

1536 Photoelectric Pick-off With the Type 1532-P2 Flash Delay and the stroboscope, permits analysis of motion of objects rotating at relatively steady speeds (paragraph 2.10.2).

1537 Photoelectric Pick-off Similar to Type 1536 Pick-off, but with no light source (paragraph 2.10.3).

1539 Stroboslave A small stroboscope without internal oscillator (paragraph 2.10.6).

1538-P4 High-Intensity-Flash Increases light output 10 times for single- Capacitor flash photographic applications (paragraph 2.11.7).

4 INTRODUCTION 1538-A Strobotac

Figure 1-3. The Type 1538, powered by the Type 1538-P3 Battery pack, offers a precise bright stroboscope capability completely independent of the ac power line. A unique advantage in use with large machine complexes such as found in textile and printing industries. The battery pack can power the Strobe for up to 8 hours of intermittent use.

INTRODUCTION 5 1538-A Strobotac

Section 2 OPERATING PROCEDURE

2.1 Opening the Case d. To secure the cable end, slide the 3-wire plug onto the 1/2-inch pin on the panel. e. To complete the closing of the case, push down To open the Flip-Tilt case: slightly on the handle of the case with one hand, and a. Set the instrument on a flat surface so that it rests with the Other swing the instrument so that the panel on its rubber feet. is facing down. Lower the instrument onto the rubber b. Unlock the case by sliding the two gray latch blocks, gasket by slowly releasing the handle. Apply light pres- (one on each side of the case) away from the handle. sure on the top of the case and slide the two gray (It may be necessary to push down on the top of the latch blocks toward the handle to lock the case. instrument to release the latch blocks). c. Using the palm of the hand, push the handle down as far as possible. With the other hand, swing the 2.3 Power Requirements instrument to the desired angle. Lower the instrument onto the rubber gasket by slowly releasing the handle. The instrument will be held in position at any angle from vertical to about 30° by its friction against the 2.3.1 Power-Line Operation gasket. However, the case is not locked in place and it may not stay in a tilted position under severe vibra- The Type 1538 Strobotac electronic stroboscope can tion. If the instrument is to be hand-held, nestle the be operated from a 115- or 230-Volt, 50- to 60-Hz or case into the cover and lock it in by sliding the latch 400-Hz line, as well as from a 24-Volt dc supply. For blocks toward the handle. line operation, one end of the ac power cable (P/N d. Disengage the 3-terminal ac-power-cable plug and 1538-0420) mates with the 4-prong plug (labelled 115 unwind the cable from around the range-switch bar V 50-60 Hz/24 VDC) on the panel and is locked in knob and the reflector. place by the two attached clips. (To unlock the clips, squeeze them toward each other with thumb and fore- 2.2 Closing the Case finger.) The input line voltage for which the instrument is wired is noted on the panel, directly above the power plug. To close the case for storage or transit of the instru- To change from 115-Volt to 230-Volt operation, re- ment, proceed as follows: move the two jumpers on transformer T501 between a. Set the range-switch knob to the 4000-25000 RPM terminals 1 and 3 and terminals 2 and 4, and add a position. jumper between terminals 2 and 3 (see Figure 2-1). b. Turn the reflector down against the panel, facing up. Replace the AC Power Plug with the correct plug for c. Push the 4-prong socket at one end of the ac power your location. A 0.25- ampere fuse is used for either cable onto the panel power plug and wind the cable in line voltage. To indicate a change to 230-volt opera- a counterclockwise direction around the range-switch tion, order an input power plate, P/N 1538-8110, from bar knob and the reflector. IET Labs. This plate, marked 230 V, 50-60 Hz, 24 VDC, can be cemented onto the panel over the 115-V marking.

6 OPERATION 1538-A Strobotac

To change the instrument from 230- to 115-volt op- 2.3.3 Type 1538-P3 A Battery Source and eration, remove the jumper on transformer T501 be- Charger tween terminals 2 and 3 and add jumpers between terminals 1 and 3 and terminals 2 and 4 (see Figure 2-1). Always be sure the power to be applied corresponds The Type 1538-P3 A Battery and Charger is avail- with the panel marking above the panel power plug. able as an optional accessory for the Type 1538 stro- The male end of the power cable has three terminals. boscope. It includes a rechargeable nickel-cadmium The third pin (ground) on the power plug has been battery and an automatic battery charger mounted added for the safety of the operator; it should not be together in a carrying case. The battery cable is per- disconnected. If a 2-way adaptor must be used, be manently attached to the unit. For battery operation, sure the instrument is properly grounded. simply mate the four-contact connector on the end of the output cable with the 4-prong plug (labelled 115 V 50-60 Hz/24 Vdc) on the panel of the stroboscope. The cable is locked to the panel by the two clips on the connector; to remove the cable, press the clips toward each other with thumb and forefinger. To charge the battery, plug the unit’s power cord into the AC line. The 1538-P3 can be ordered, or modified for, 220 V operation in the same manner as the 1538.

THE BATTERY The battery consists of 20 sealed cylindrical Ni-Cd. cells, which supply 24 volts at 2.3 ampere-hours. The cells incorporate a resealing, safety vent mechanism that will not open during normal battery usage but, should excessive gas pressure build up within the cell, the vent opens at a predetermined internal pressure. This pressure buildup causes distortion of the O-ring Figure 2-1 The transformer terminals on the and creates a path to the atmosphere. When pres- stroboscope are numbered as shown. sure within the cell returns to atmospheric pressure, the O-ring returns to its original shape and position 2.3.2 Battery Operation and reseals the opening. THE CHARGER The stroboscope will also operate on 24 volts dc. The The charger included in the Type 1538-P3 A Battery Type 1538-P3 Battery and Charger is recommended Source and Charger is a constant-current type with for this type of operation (see paragraph 2.3.3). The microprocessor-controller charging and supervision. dc power also is applied at the 4-prong plug on the One end of the power-line cable is permanently at- panel, and is controlled by the ON-OFF, POWER tached to the charger. switch. The 0.25-ampere fuse in the stroboscope is not in the circuit for dc operation, but protection is When the battery is fully charged the charger will maintained by the 1-ampere fuse mounted on the bat- switch automatically to trickle charge, which will con- tery case. tinue until it is unplugged from the ac line. When first The Type 1538 cannot be calibrated when operating received, the battery should be charged for about 10 on dc power. Calibration on ac (refer to paragraph hours. A completely discharged battery can be 2.7) is valid for both ac and dc operation and will hold charged to 70% of full capacity in 10 hours. A fully for a long period of time. charged battery will power the Type 1538 for about 8

OPERATION 7 1538-A Strobotac

hours of normal, intermittent operation, after which a 2.4 Turning the Instrument On 10-hour, overnight charge should be adequate to return the battery to 100% capacity. If the maximum After connecting the power cable to the power line, operating time has been approached, a full 14-16 hours or connecting the 1538-P3 to the instrument, pivot will be required to recharge the battery to full capac- the reflector assembly to an upright position and turn ity. With no warm-up time required by the Type 1538, the POWER switch ON. The stroboscope is ready the POWER switch should always be turned OFF for use immediately. when the instrument is not in use, to conserve the charge. Although the life of the battery cells may be some- what shortened by continual overcharging in the con- 2.5 Positioning the Stroboscope stant-current mode, they can be left on trickle charge for an indefinite period. The cell life of the battery is The light beam can be aimed in almost any direction reduced by repeated complete or nearly complete dis- by means of the swivel arm and the rotating reflector charging of the battery, or by severe overcharging. (1, Figure 1-2). The intensity of the light pulse is so Under average operating conditions, the number of high and the beam angle is so small that it is usually charge/discharge cycles may exceed 5000 before not necessary to place the unit close to the object replacement of the battery becomes necessary. How- being viewed. If the instrument is to be held in a fixed ever, if the battery is deeply discharged, a cycle life position for a long period of time, a tripod or other as low as 300 may result. If the state of charge of the support should be used. battery is unknown, recharge it for ten hours. Con- tinuous trickle charging will maintain 100% capacity of the battery during prolonged storage periods. The 2.6 Adjusting the Flashing Rate battery will discharge with time if trickle charging is not used; the rate of discharge depends on the stor- The flashing rate of the strobotron lamp is adjusted age temperature, as shown in Figure 2-2. by means of the RPM range-switch knob and the RPM dial (5 and 7, Figure 1-2). The total range of the stroboscope is divided into four overlapping ranges selected by the range-switch knob. The limits for each range are marked near the appropriate window in the range mask. The windows on the mask reveal only the range in use. To operate the RPM dial, turn the fluted, transparent rim that surrounds the range-switch mask. The red indicator line over the dial scale gives the speed setting in flashes per minute (corresponding to rpm) for speed measurements.

2.7 Calibration

To use the stroboscope for the most accurate measurements of speed, the RPM dial can be calibrated Figure 2-2. Typical charge- retention characteristics using the frequency of the ac power line. The cali- of the battery. bration is then valid for either ac or battery operation. There is no provision for calibrating the instrument on battery power.

8 OPERATION 1538-A Strobotac

To calibrate the Type 1538, proceed as follows: 2.8 Speed Measurements a. Allow the instrument to warm up for at least ten minutes. b. Turn the RPM range switch to the CAL position. c. Set the RPM dial to 3600* (60 cycles/second x 60 2.8.1 Fundamental-Speed Measurement seconds/minute) by rotating it until the mark at 3600* is exactly under the red indicator line. If the speed of the object being viewed is not known d. Adjust the panel screwdriver control marked HIGH at least approximately, start at a high flashing rate CAL until the flashing of the neon CALIBRATE lamp where multiple images result and reduce the flashing stops (or nearly stops). The lamp may remain on, rate until a single image is obtained. The first single off, or barely on, but it should not be changing. The image occurs when the flashing rate is equal to the longer the time required for the lamp to complete one rotational speed of the object and the speed can then cycle — from on to off, then on again — the closer be read directly from the RPM dial. the setting of the potentiometer is to an exact calibration. For example, if the CALIBRATE lamp takes IMPORTANT two seconds to complete one full cycle, with the RPM To determine that a single image has been obtained, dial set at 3600, the error in the dial calibration is: the object being viewed must have some identifying 3600* rpm mark to provide non-symmetry. For instance, a four- = 30 cycles/min (rpm) 60 cycles/sec x 2 sec/cycle bladed fan must have a mark on one blade only, or a piece of tape can be applied to one tooth of a gear to produce the images shown in Figure 2-3. NOTE Do not confuse the characteristic flicker on low On the three lower-speed ranges, a quick check on ranges with the on-off action referred to here. whether or not the stroboscope is flashing at the fun- When the CAL setting is very close to the power- damental speed of the device being measured can be line frequency, the CAL lamp will vary in inten- made by simply switching to the next range without sity very slowly. moving the RPM dial. Since the ratio between ranges is approximately 6:1, six images will appear at the e. Set the RPM dial to 900** and repeat step d, using next higher range when the stroboscope has been set the LOW CAL screwdriver adjustment on the front to the fundamental speed. If only three images ap- panel. On this range, for example, a two-second flash- pear, for example, the stroboscope has been set to ing period of the CALIBRATE lamp represents an one-half the correct frequency. On the high-speed error of: range, double the speed setting of the RPM dial to 900 rpm check for fundamental-speed operation. A double = 7.5 cycles/min (rpm) 60 cycles/sec x 2 sec/cycle image will occur when the frequency setting is doubled. If the fundamental speed of the device be- f. Return the RPM dial to 3600* and repeat the pro- ing measured is above 75,000 rpm, it is not possible to cedure of step d until the CALIBRATE lamp is flash- check for the correct speed setting by this method. In ing very slowly or not at all. (This step is not neces- this case, refer to paragraph 2.8.3. sary unless the LOW CAL adjustment was changed significantly.) g. In general, it is not necessary to return to the 900** RPM point to repeat the procedure unless a very precise calibration is required. The RPM dial is now calibrated to within ±1 percent on all ranges.

•3000, if 50-Hz line is used. ••750, if 50-Hz line is used.

OPERATION 9 1538-A Strobotac

Gear not marked for speed measure- multiple rate or at the fundamental rate, as described ment. Simple observation is possible in paragraph 2.8.1. but observer cannot be certain if im- Where convenient, switching to a lower range with age is single or multiple. its submultiple flashing rate (approximately 1/6 of the fundamental frequency) will often prove helpful because of the brighter image obtainable. Single image observed with tape ap- Submultiple flashing is necessary to observe or mea- plied to one tooth of gear. sure the speed of objects moving at rates above 150,000 rpm. Refer to paragraph 2.8.3 for the method of determining the fundamental speed when submultiple operation is necessary. Multiple (double) image observed with At flashing rates between integral submultiples, mul- tape applied to one tooth of gear. Im- tiple images will be observed. Table 2-1 gives some ages are 180° apart. (Stroboscope is examples of submultiple speeds and the correspond- flashing twice in one revolution of the ing number of images produced for a fundamental gear.) speed of 180,000 rpm. Note the numerical relationship between the numerator of the submultiple frac- Multiple (triple) image observed with tion and the number of images. This relationship is tape applied to one tooth of gear. Im- true for all submultiple speeds. ages are 120° apart. (Stroboscope is flashing three times in one revolution of the gear.) Table 2.1 Relationship between submultiple speed settings and Figure 2-3. Stroboscopic images produced by a number of images produced for a fundamental speed rotating gear. of 180,000 rpm.

NOTE Submultiples of Number of Reading of Multiple images will always be observed when the Fundamental Speed Images Range Switch flashing rate of the stroboscope is set to a multiple of (180,000 rpm Assumed) Produced RPM Dial the fundamental speed of the object. As the flashing 1 1 180,000 rate is reduced from a rate higher than the funda- 5/6 5 150,000 mental speed of the object, the first single image will 4/5 4 144,000 appear when the flashing rate is equal to the funda- 3/4 3 135,000 2/3 2 120,000 mental speed. Make the quick check described above 3/5 3 108.000 to be sure that the first single image has not been 1/2 1 90,000 missed. 2/5 2 72,000 1/3 1 60.000 1/4 1 45,000 1/5 1 36,000 2.8.2 Submultiple Speed Measurements 1/6 1 30.000

When the flashing rate is below the fundamental speed of the object, single and multiple images will be ob- 2.8.3 Measurement of Speeds above 150,000 served. If the stroboscope flashes at an integral sub- RPM multiple of the speed of the rotating object under observation (such as 1/2, 1/3, 1/4, 1/n), the motion of the By means of submultiple synchronization, speeds up object will be ”stopped,” showing a single image, just to about 1 million rpm can be measured accurately as it will at the fundamental speed. If speed mea- with the stroboscope. The procedure is as follows: surements are being made, it is necessary to deter- a. Starting at 150,000 rpm, decrease the flashing rate mine whether the stroboscope is flashing at a sub-

10 OPERATION 1538-A Strobotac

of the stroboscope by turning the RPM dial clock- 2.8.5 Slow-Motion Studies wise until a single image is obtained. Record the reading of the RPM dial and call it X. High-speed motion can be reproduced by the strobo- b. Observe the stroboscopic images as the reading of scope at an apparently much lower speed if the cy- the RPM dial is slowly decreased. Stop when the next clic or reciprocating motion occurs at a constant rate. single image appears. Record the new reading of the If the flashing rate of the stroboscope is set at a speed RPM dial and call it Y. slightly lower than the fundamental speed of the ob- c. Calculate the harmonic number, n, by n = Y X-Y served object, the object will appear to move slowly in the same direction as the actual motion, as noted in Round off the value of n to the nearest whole number. paragraph 1.2, at a speed equal to the difference be- d. Calculate the fundamental speed, S , by S = nX. f f tween the actual speed of the object and the flashing For example, if the first single image occurs at rate of the stroboscope. If the flashing rate is set X = 77,200 rpm and the second single image occurs slightly higher than the speed of the object being ob- at Y = 58,000 rpm, then served, the same slow motion will result, but in the opposite direction. n = 58,000 = 3.02 77,200 - 58,000 This stroboscopic technique of slowing down motion can be extremely useful in investigating the operation Rounded off to the nearest whole number, n = 3. The of a device under normal operating conditions. Ex- fundamental speed is then cessive vibration, misalignment of parts, mode of vibration of equipment on a shake table, operation of S = 3 x 77,200 = 231,600 rpm. f vibrating reeds, actual relation between traveler and thread during a complete revolution of the traveler on There is a nomogram at the end of this section that a textile spinning frame - these are a few examples may be used for this purpose. of the many slow-motion studies that are possible with the Type 1538. 2.8.4 Low-Speed Operation 2.9 Type 1538-P2 Extension Lamp The measurement of speeds on the low range of the instrument (below about 600 rpm) is complicated by For use in spaces too small for the complete strobo- the flicker resulting from the inability of the eye to scope, the Type 1538-P2 Extension Lamp (Figure carry over the image from one flash to the next. Such 2-4) is a convenient accessory. The lamp and reflec- measurements should be made in a darkened envi- tor in this assembly are identical to those on the ronment to reduce the disconcerting effect of high Strobotac. The assembly is supplied with a six-foot ambient room lighting on the observed pattern. Dark cord and a plug that mates with the panel socket glasses, worn by the operator, may prove helpful. marked EXT LAMP. When plugged in, the Exten- Speeds below 110 rpm can be measured by means of sion Lamp flashes instead of the lamp on the strobo- multiple images. For example, if the flashing rate of scope. This accessory makes it possible to mount the the stroboscope is twice the fundamental speed of lamp in small out-of-the-way places such as test cham- the device, two images, 180 degrees apart, will ap- bers and to control it from a safe distance. pear. At three times the fundamental speed, three Additional cable up to 50 feet long can be used with images, 120 degrees apart, will appear, etc. the Extension Lamp. The cable and connectors are This multiple-image technique can also be used for available from IET Labs, Inc. However, when addi- higher speeds, within the range of the stroboscope, tional cable is used, the peak intensity of the flash where flicker makes it difficult to tell when the cor- decreases. For instance, with a 25-foot cable, the peak rect flashing rate is obtained (for example, between light output is reduced to one fourth of its original value, 110 and 600 rpm). the flash duration is doubled, and the total light output is reduced to one half.

OPERATION 11 1538-A Strobotac

NOTE Connect the external signal to the INPUT jack on the The Type 1538-P2 Extension Lamp and the Type panel; use the standard phone plug supplied. Starting 1538-P4 High-Intensity-Flash Capacitor cannot be at the fully clockwise position, adjust the RPM dial used simultaneously. until satisfactory synchronization is obtained. For large-amplitude inputs there will be a wide range of settings for the RPM dial at which the instrument will operate satisfactorily. For small-amplitude inputs, the range will be correspondingly smaller.

2.10.2 Type 1531-P2 Flash Delay and type 1536 Photoelectric Pick-off

Two very useful accessories for the stroboscope are Figure 2-4. Type 1538-P2 Extension Lamp. the Type 1531-P2 Flash Delay and the Type 1536 Photoelectric Pick-off. The combination of these three instruments (Figure 2-5) makes it possible to synchro- 2.10 External Synchronization nize the flash of the Type 1538 with the moving object at any desired point in the cycle of operation of the object. These synchronizing devices can operate at very high speeds and do not load the machine un- 2.10.1 Use of the Input Jack der observation. The Type 1531-P2 Flash Delay is a small, portable, The instrument can be triggered by any electrical sig- time-delay unit, used to insert a controlled delay pe- nal of at least 1 volt, peak-to-peak, (to a maximum of riod between an externally generated trigger pulse 10 volts rms) applied at the INPUT jack. For sine- and the resulting light flash from the stroboscope. The wave inputs, the unit will operate with a 0.35-volt (rms) flash delay also provides a convenient method of ob- signal down to 100 Hz. Below this frequency the re- taining single-flash photographs at any desired point quired amplitude increases to 3.5 volts at 5 Hz. For in the cycle of the moving object. pulse inputs (i.e., step-wavefront signals), the repeti- The Type 1536 Photoelectric Pick-off is used to con- tion rate can have any minimum value. The instru- vert the motion of an object to electrical impulses that ment can be synchronized with external signals at fre- can be applied to the stroboscope. It consists of a quencies up to at least 150,000 rpm (2.5 kHz). Be- light source, a simple cylindrical optical system, and a cause a positive-going signal is required at the input photocell. Variations in reflectivity, produced by the to flash the stroboscope, positive pulses are required motion of the object being observed, produce electri- to synchronize on the leading edge. Negative pulses cal signals that are amplified, delayed, and shaped by will result in a delay depending on the trailing-edge the Flash Delay, and are then fed to the stroboscope. characteristics of the input pulse. Power for both the photocell and the lamp are sup- To operate the stroboscope from an external electri- plied by the Type 1531-P2 Flash Delay. cal signal, set the RPM range switch so that the fre- The reader should refer to the Appendix of this book rpm and to the Operating Instructions for the Type 1531- quency of the driving signal (f= 60 ) does not exceed the maximum frequency indicated on the range mask. P2 Flash Delay and the Type 1536 Photoelectric Pick- Set the FLASH CONTROL switch to EXTERNAL. off for further information concerning these instruments and their use with the Type 1538 Stroboscope.

12 OPERATION 1538-A Strobotac

up to 18 million beam candles when used for single- flash applications. The reader should refer to the In- struction Manual for the Type 1539 Stroboslave. Com- plete specifications are included in the Appendix of this book.

2.10.5 Use of Multiples Stroboscopes

When a multiple source of flashing light is needed, several Type 1538 stroboscopes can be connected together. A cable from the OUTPUT jack of the first instrument connects to the INPUT jack of another, Figure 2-5. A widely used combination consists of and so on. Connected in this manner, the stroboscopes the stroboscope with the Type 1531-P2 Flash Delay will flash at the same time. and the Type 1536 Photoelectric Pick-off. Types 1531 and 1546 Strobotac electronic stroboscopes can be substituted for any of the Type 1538 2.10.3 Type 1537 Photoelectric Pick-off instruments for this multiple use. However, a Type 1531-P4 Trigger Cable (with built-in transformer) must be used at the OUTPUT of each Type 1531 to The Type 1537 Photoelectric Pick-off differs from prevent overload and possible damage to the input the Type 1536 in that no light source is included. The circuitry of the 1538 and 1546 units. photosensitive element is a silicon light-activated switch. This pick-off will trigger the type 1538 Stro- boscope directly. Refer to the Instruction Manual for 2.10.6 Connecting the Accessory Instruments the Type 1537 for further details on the operation of this accessory; its specifications are given in the Ap- Figure 2-6 shows the Type 1538 Strobotac electronic pendix of this manual. stroboscope and the connections for some of the many possible combinations of accessory instruments. 2.10.4 Type 1539 Stroboslave

The Type 1539 Stroboslave is an inexpensive, minia- ture, electronic stroboscope. It has no internal oscillator for setting the flashing rate, and so it must be triggered by an external device. It cannot be used for direct measurement of rotational speed. This small stroboscope is suitable for high-speed-photography applications and motion studies other than tachometry. The Stroboslave will flash upon closure of external contacts or upon reception of a 2-volt positive pulse at its panel INPUT jack. It will operate directly from the OUTPUT jack of the Type 1538 Strobotac. The lamp and reflector of the Stroboslave are connected to the unit by a five-foot flexible cable, to permit posi- Figure 2-6. Some of the many possible tioning the lamp close to the moving object. Operat- combinations of the Type 1538 Strobotac electronic ing over a range of 0 to 25,000 flashes per minute, the Stroboscope and its accessory instruments. Type 1539 produces a peak light intensity of up to 11 million beam candles on the HIGH-intensity range and

OPERATION 13 1538-A Strobotac

2.11 High-Speed Photography Figure 2-7. Plot of light intensity vs time of the Type 1538 Stroboscope.

2.11.1 General

The short duration of the flash of light from a stroboscope makes it ideal for high-speed-photography applications. To control the exposure time, the camera shutter can be left open and the light turned on and off very quickly. With the use of convenient controls for triggering, such as a photocell or microphone, the 2.11.3 Beam Type 1538 can be used for single flash or can be set to flash at a given rate for multiple exposures. The With the standard reflector in position on the peak flash intensity of the Strobotac varies with the Strobotac, the light output is concentrated in a 10- flashing rate, from about 200,000 candela at the high- degree beam (measured at 1/2-peak-intensity points), est flash rate to several million candela at low speeds. whose apparent source is 18 inches behind the front When it is desirable, even greater single-flash light of the reflector. Outside this 10-degree cone the light intensity (to 44 million candela) can be obtained by intensity falls off sharply, so that the area of reason- addition of the Type 1538-P4 High-Intensity-Flash ably constant illumination is not large. If this beam Capacitor, an optional accessory that plugs directly width is not adequate to light the subject, the reflec- into the Type 1538 Strobotac (refer to paragraph 2.11.7). tor can be easily removed and the bare lamp used to illuminate the area. 2.11.2 Flash Duration 2.11.4 Spectral Characteristics The duration of the stroboscope flash can vary from 0.5 to 8 microseconds, depending on the flash-rate- The spectral distribution of the flash of the Strobotac range setting (refer to Table 2-2). (shown in Figure 2-8) is excellent for photography with both orthochromatic and panchromatic films. Table 2-2 Equivalent color temperature of the flash is about 6500 Flash duration at 1/3 peak intensity for each range of to 7000 degrees Kelvin. the Type 1538 Strobotac.

RPM Range Switch Flash Duration Setting (Microseconds) 110-690 3 670-4,170 1.2 4,000-25,000 0.8 24,000-150,000 0.5

Figure 2-7 shows a plot of light intensity versus duration time. When the Type 1538-P4 High-Intensity- Flash Capacitor is used to produce extra-bright single flashes, duration is increased to 8 microseconds. Figure 2-8. Spectral distribution of the Strobotron’s light output.

14 OPERATION 1538-A Strobotac

2.11.5 Exposure Data 2.11.7 Type 1538-P4 High-Intensity-Flash Capacitor Figure 2-9 can be used to determine the guide number for a given film speed when the Type 1538 An optional accessory for the Type 1538 Strobotac is Strobotac or Type 1539 Stroboslave is used. the Type 1538-P4 High-Intensity-Flash Capacitor To determine the effective lens aperture (f setting), (Figure 2-10). With this accessory connected, a single divide the guide number by the stroboscope-to-sub- 8-microsecond flash of 44 million candelas can be ject distance (in feet) plus 1.5 (refer to para- obtained. graph 2.11.3). The guide numbers are given rather than the watt- second ratings, because the latter cannot be used to determine the subject illumination without a full knowl- edge of the reflector characteristics and the tube ef- ficiency.

Figure 2-10. The Type 1538-P4 High-Intensity-Flash Capacitor can be used with the Strobotac for short, single flashes.

This is used when a brighter flash is needed to photograph an object moving at an extremely high speed or one in high ambient light. The circuit for the Type 1538-P4 Capacitor is given in Figure 2-11. To attach the Capacitor to the stroboscope, open the Flip-Tilt cabinet fully, as shown in the lower right-hand view of Figure 1-1. Place the Type 1538 on its side. Attach the Capacitor to the base section of the Flip-Tilt cabi- 2.11.6 Single-Flash Photography net. To do this, line up the screw in the center of the capacitor with the tripod-mounting hole in the bottom With single-flash photography, the camera shutter is of the Flip-Tilt cabinet. Tighten the screw, locking the opened, the stroboscope is flashed once, to expose capacitor in place. Set the stroboscope upright and the film, and the shutter is closed again. Single-flash plug the cable into the 4-prong socket marked EXT pictures, taken in this manner, have solved many LAMP, on the panel of the stroboscope, as in Figure 2-12. puzzling industrial problems. The subject is photo- The assembly is now ready for single-flash opera- graphed in the position it occupies at the instant the tion. The maximum flashing rate with the combina- stroboscope lamp flashes. tion is 60 flashes per minute. The Capacitor is automatically discharged when the 4-prong plug in the EXT LAMP socket is removed. The Capacitor can also be discharged by changing the setting of the NOTE RPM range switch. Guide numbers for various film Because the first trigger pulse from the oscillator is speeds when the Capacitor is used with the strobo- used to charge the flash capacitor, always trigger the scope are given in Figure 2-9. The reader should note stroboscope once or twice before actually taking a the instructions in paragraph 2.11.6 for single-flash single-flash photograph. The capacitor will then be photography. The Type 1538-P4 High-intensity-Flash charged, ready to flash the lamp on all subsequent Capacitor and the Type 1538-P2 Extension Lamp trigger pulses. cannot be used simultaneously with the stroboscope.

OPERATION 15 1538-A Strobotac

To use the nomogram, find the point on the X scale corresponding to the highest flashing rate at which a true stopped-motion image occurs. Then find the point on the Y scale where the next lower true stopped image occurs. Hold a straightedge so that it intersects the X and Y scales at the points plotted. The straightedge should intersect the n scale at an integer. Multiply the X scale value by this integer to Figure 2-11. Circuit of type 1538-P4 High-Intensity- determine the fundamental speed. Flash Capacitor. Example:

NOMOGRAM FOR USE IN MEASURING Suppose that the first time stopped-motion image is SPEEDS BEYOND THE FLASHING obtained at 150,000 rpm, the next lower one at 120,000 RATE OF THE TYPE 1538 STROBOTAC rpm. A line drawn through 150 on the X scale and 120 on the Y scale intersects the n scale at 4. There- The nomogram below can be used to determine quickly fore the fundamental speed is 4 x 150,000, or 600,000 rpm. the fundamental speed of an object from two succes- sive submultiple images.

16 OPERATION 1538-A Strobotac

Section 3 PRINCIPLES OF OPERATION

3.1 General After this tremendous pulse of light, the tube requires about 150 microseconds to deionize. The voltage across the tube must remain less than 80 volts during If a cyclically moving object is viewed by a light that this deionization time or holdover will result. is flashing at or near the cyclic rate of the object, the latter will appear stationary or in slow motion. The optical illusion thus produced depends on the periodic 3.3 The Charging Circuit observation of the object. If the flashing rate of the light is adjusted to produce a stationary image, the The necessary deionization time limits the maximum flashing rate equals the cyclic speed of the moving flashing rate of the stroboscope. Figure 3-1 illustrates object. The stroboscope is essentially a source of the problem. The curves labeled R-C and L-C show flashing light with an adjustable calibrated control of the effects of charging the capacitor through a resis- flash frequency. In most modern stroboscopes the tor and an inductor, respectively. The slopes required actual flash occurs inside a xenon-filled tube. The gas to keep the voltage below the 80-volt deionization level is ionized by the rapid discharge of a capacitor. The would impose delays in reaching the firing level, which gas must then deionize before the next flash can oc- in turn would restrict the maximum flashing rates to cur. This deionizing time sets a limit on the maximum 24,000 and 54,000 flashes per minute, respectively, flashing rate. If voltage is applied across the tube for the particular tube and voltages used in the Type before the gas is deionized, continuous conduction 1538. The answer to this problem is to hold the volt- known as “holdover” occurs. age at zero for the deionization period and then to raise it quickly to the firing level. 3.2 The Strobotron Tube The new circuit shown in Figure 3-2 provides an almost ideal charging curve (labeled “Type 1538” in Figure 3-1). During the 150-microsecond deioniza- As used in a stroboscope, the strobotron tube con- tion time after the strobotron has flashed, the transis- tains two main electrodes, a cathode and an anode, tor (which acts as a switch) is saturated and the trans- separated by 3/8 inch, in an envelope filled with xe- former primary current increases, storing energy in non gas at a pressure of one-half atmosphere. A spe- the transformer core. The voltage induced in the sec- cially designed capacitor acts as a low-impedance ondary winding during this buildup is blocked by the source to supply 800 to 1000 volts across these elec- diode rectifier, and no voltage appears across the ca- trodes. The gas, however, remains nonconducting until pacitor and strobotron tube. At the end of this 150- a 5000-volt pulse is applied to trigger wires inter- microsecond interval, the transistor is switched off, spersed between these main electrodes. This trigger and the primary current goes to zero. The collapsing pulse ionizes the gas, and causes up to 1000 amperes magnetic field generates a reverse-polarity voltage in to flow through it. This peak flow of almost one mil- the secondary, causing the diode to conduct and the lion watts generates an intense flash of white light of stored energy to be transferred to the capacitor. 15 million beam candles.

Principle of Operation 17 1538-A Strobotac

When the energy in the transformer is zero, the cur- Moreover, the use of a transformer as the inductive rent again reverses and the diode appears as an open element permits the use of a low-voltage transistor circuit, leaving all the stored energy in the capacitor. circuit to generate the high voltage required by the This transfer can be made as fast as one wishes, and strobotron tube. A block diagram of the complete cir- the flashing rate can therefore be made to approach cuit is shown in Figure 3-3. A transistorized RC oscil- the theoretical maximum. lator sets the flashing rate of the stroboscope. Once each cycle, a transistor trigger circuit generates a 5- kilovolt, 5-µs pulse to trigger the strobotron tube. In the time between these pulses, the main discharge capacitor (which varies from 0.007 µF on the high range to 1.5 µF on the low range) must be recharged to 800 volts. The monostable circuit, triggered by the oscillator, generates a 200-µs pulse that saturates the transistor switch, stores energy in the transformer, and allows the strobotron to deionize. At the end of the 200-µs pulse, sufficient energy has been stored to resonantly charge the capacitor to 800 volts in an additional 200 µs. Thus, a maximum flashing rate of 1 µs or 2500 flashes per second is possible. 400

Figure 3-1. Voltage-vs-time characteristics of various charging circuits.

Figure 3-3. Block diagram of the Type 1538 Strobotac electronic stroboscope. Figure 3-2. Charging circuit of the Type 1538 Strobotac electronic stroboscope. The average light output of a stroboscope varies di- The transfer of energy from the power supply to the rectly with flashing rate and discharge capacitance. intermediate storage inductor, and then resonantly to The exceptionally wide flashing-rate range the discharge capacitor, can be made with an effi- of the Type 1538 (1500 to 1) would mean a drastic ciency approaching 100%. In the conventional RC variation in light output if only one discharge capaci- charging circuit, however, half of the available en- tor were used. On the other hand, a continuously ad- ergy is dissipated in the charging resistor regardless justable discharge capacitor with a 1500-to-1 range of the value of the resistor (including zero ohms). The was obviously impractical. The compromise solution use of inductive charging saves the power ordinarily was to switch in a different capacitor for each of the dissipated in the charging resistor and reduces power four 6:1 speed ranges. The resulting capacitance varia- requirements, so that battery operation is practical. tion is 216 to 1, and this raises another design problem.

18 Principle of Operation 1538-A Strobotac

If the discharge capacitor varies in value over a 216- 3.4 The Calibration Circuit to-1 range, then, in the resonant charging circuit dis- cussed earlier, either the inductance must also vary To calibrate the RPM dial against the power-line fre- by a factor of 216 or the current must vary by a fac- quency, voltages at both the power-line and the flash- tor of 216 to supply sufficient energy per cycle. Large ing-rate frequencies are superimposed across a neon coils and 30 A current were both unappealing, so an- lamp (V901). When the flashing rate equals the other approach was found. power-line frequency or a submultiple of it, the volt- On lower-speed ranges, however, where the dis- age across the lamp remains constant and the lamp is charge capacitance is higher, the energy stored in the in a condition of steady intensity. Depending upon the transformer is insufficient to produce the desired 800- phase relationship between the strobotron flashing rate volt firing potential. On these ranges, the 200-µs de- and the power-line frequency, the steady-intensity lay following the monostable circuit generates a trig- condition of the neon lamp may be maximum inten- ger pulse occurring 200 µs after the end of the sity or zero intensity. If the flashing rate of the stro- monostable pulse, to retrigger the monostable circuit. botron differs from the power-line frequency, the av- Thus a single pulse from the oscillator starts a train of erage voltage across the neon lamp will vary, and the 200-µs pulses in the monostable circuit and its delay intensity will change at the difference frequency. loop. Each of these pulses stores energy in the inductor that is repeatedly transferred to the capacitor during the time between pulses. Each pulse raises the capacitor voltage in a small step, as shown in Figure 3-4. This process continues until the capacitor is charged to 800 volts. At each step, a voltage pulse equal to the capacitor voltage divided by the transformer turns ratio appears across the Zener diode on the transformer primary. When the capacitor reaches 800 volts, the diode voltage is exceeded and the flip- flop closes the gate. This breaks the feedback loop and ends the pulse train started by the oscillator. While this multiple-cycle resonant-charging technique used on the lower ranges requires more time than the single- cycle charge, a correspondingly longer time is available in which to recharge the capacitor.

Figure 3-4. The voltage buildup on the charging capacitor is in small steps.

Principle of Operation 19 1538-A Strobotac

4.6 Replacement of Mechanical Parts 4.6.3 Swivel-Support Assembly, Pivot Blocks, and Washers

4.6.1 General To replace the swivel-support assembly (see Figure 4-10): a. Remove the reflector and the strobotron lamp; then remove the instrument from its case. Although the stroboscope is designed especially for b. Loosen (do not remove) two nuts (A, Figure 4-10) use in manufacturing, testing, and other areas where and slide the two pivot blocks apart. (The heads of the working environment is often unsuitable for pre- the two screws (B) clamp the pivot blocks in position cision electronic instruments, certain mechanical parts when nuts (A) are tightened.) mounted on the outside of the instrument case may c. Unsolder the three swivel-support assembly leads eventually become contaminated or damaged. To re- (X, Y, Z) and remove the assembly. place these parts (see Figure 4-9), refer to the fol- d. The pivot blocks and washers can now be replaced. lowing instructions. e. Position the new swivel-support assembly so that the strobotron tube socket and leads (X, Y, Z) are as 4.6.2 Reflector and Cover shown in the figure. f. Insert leads (X, Y, Z) through the slot between screws (B), and hold the swivel-support assembly in Remove the old reflector by pulling it off the swivel- position between the two pivot blocks. support assembly. Mount the new reflector by sliding Slide the pivot blocks together and tighten nuts (A). it onto the assembly until the spring-loaded detent The pivot action of the swivel-support assembly may button snaps into the groove inside the reflector base. need readjustment; if so, loosen either nut (A), adjust To replace the reflector cover, remove the old cover the corresponding pivot block, and retighten the unit. by pushing on the edge at each of the molded-in clips g. Solder leads (X, Y, Z) to the terminals, as shown. that clamp over the rim of the reflector housing; the cover will snap off. Then mount the new cover by pulling its edge toward the rim of the reflector housing until the three clips snap securely into place.

Figure 4-10. Interior view showing mounting of the swivel-support assembly, pivot blocks, and connections.

Figure 4-9. Miscellaneous part numbers.

26 MAINTENANCE 1538-A Strobotac

4.6.4 Scale Mask Assembly

To replace the Scale Mask Assembly: a. Set the range switch to the 4000-25000 RPM position. b. Loosen the two setscrews in the Scale Mask As- sembly hub and remove the assembly from the range- switch shaft. c. Mount the new Scale Mask Assembly on the shaft and center the 4000-25000 RPM window in the dial over the white panel segment beneath the dial. d. Tighten both setscrews securely.

4.6.5 Dial

To replace the Dial: Figure 4-11. Name and location of parts included in the IET Flip-Tilt Case (refer to table 4-1). a. Remove the instrument from the case. Heed the warning of paragraph 4.4.3 (to prevent contact with Table 4-1 800 volts). Part numbers for the flip-tilt case b. Set the range switch to the 4000-25000 RPM position and remove the Scale Mask Assembly (refer to IET paragraph 4.6.4, steps a and b). Name Part No. c. Note the approximate dial setting and remove the Cabinet 1538-1080 dial from the potentiometer shaft without turning the Spacer 4170-0900 shaft. To remove the dial, loosen the two setscrews Pivot Stud 4170-1267 in the dial hub, under the instrument panel. Screw 7080-0800 d. Mount the new dial at the approximate setting noted Handle Assembly 1538-2040 in step c, Tighten one setscrew in the dial hub. Cover Assembly 1538-2049 Screw 7080-0800 CAUTION Washer 8050-1500 The dial should not rub against the panel when ro- Mounting Plate 7860-1880 tated; allow a minimum clearance of 1/16 inch. (Inst. Plate) Stud 4170-1200 e. Rotate the dial from the limit stop in one direction Slide 4170-1271 to the limit stop in the other direction. Note the dis- Handle 5360-5881 tance between the red marker and each end of the Mounting Plate 7864-8010 4000-25000 RPM scale. (The ends of the scale should (Nameplate) travel approximately 1/4 inch beyond the red marker.) Washer 8140-0102 Adjust the dial until the red marker is equidistant from Slide Washer 4170-7030 each end of the scale. f. Tighten both setscrews in the dial hub. NOTE: Tighten 10-32 screws to 20-25 in. lbs torque. g. Mount the Scale Mask Assembly (paragraph 4.6.4, Bend mounting plate to give 1/32 to 1/16 spacing, both steps c and d] and remount the instrument in the case. sides. h. Calibrate the stroboscope before making speed measurements.

MAINTENANCE 27 1538-A Strobotac

Figure 4-12. Power supply etched-board assembly. Figure 4-14. Switch-circuit etched-board assembly. (Complete assembly is P/N 1538-2751). (Complete assembly is P/N 1538-2721.)

NOTE: The number appearing on the foil side is not NOTE: The number appearing on the foil side is not the part number. The dot on the foil at the transistor the part number. The dot on the foil at the transistor socket indicates the collector lead. socket indicates the collector lead.

Figure 4-13. Oscillator etched-board assembly. (Complete assembly in P/N 1538-2710.)

28 MAINTENANCE 1538-A Strobotac

ELECTRICAL PARTS LIST

CHASSIS MOUNTED PARTS P/N 1538-3000

REFDES DESCRIPTION PART NO. FMC MFGR PART NO. C 901 CAPACITOR 1538-0440 24655 1538-0440 F 901 FUSE SLC-BLCK 1/4A 250V 5330-0700 75915 313 -250 J 901 PHONE GNC .281L 2 CK T 4260-1030 82389 111 J 902 PHONE GNC .281L 2 CK T 4260-1030 82389 111 P 901 LAMP BAYONET BASE 28V .04A 560C-1000 24455 1819 PL 901 RECPT JCNES 4 CCNT MALE 4220-4400 71785 P-004-AB Q 901 TRANSISTOR 2N4906 8210-1172 04713 2N4906 R 902 RES COMP 4.3 K OHM 5PCT I/2W 6100-2435 81349 RCR20G432J S 901 SWITCH TOGGLE 2PCS DPCT STEADY 7910-1500 04009 83054 S 902 SWITCH TOGGLE 2PCS DPST STEADY 7910-1300 04009 83053 S 903 SWITCH ASM 1536-3070 24655 1538-3070 SO 901 SOCKET MULTIPLE 1536-8090 24655 1538-8090 T 901 TRANSFORMER ASM 1538-2000 24655 1538-2000 V 901 LAMP NEON NE-2L 8390-0310 24455 3AD V 902 1539-P1 REPLACEMENT FLASH LAMP 1538-9601 24655 1538-9601

OSCILLATOR PC BOARD P/N 1538-2710 C 101 CAP MYLAR .1UF 10 PCT l00 V 4860-8250 56289 410P 0.1 UF 10PCT C 102 CAP CER DISC 2200PF 10PCT 500V 4406-2228 72982 0871082Z5D00222J C 103 CAP CER D1SC.01UF 80/20PCT 500V 4406-3109 72982 0811082Z5U00103Z C 104 CAP CER DISC 390PF SPCT 500V 4404-l395 72982 0831082Z5D00391J C 105 CAP CER DISC 2200PF 10PCT 500V 4406-2228 72962 0871082Z5D00222J C 106 CAP CER DISC.022 UF 80/20PCT 500V 4407-3229 72982 0841087Z5U00223Z C 107 CAP TANT 1.0 UF 20PCT 35V 4450-4300 56289 150D105X0035A2

CR 101 DIODE 1N4154 25PIV IR .1UA SI 6082-1012 14433 1N4154 CR 102 DIODE 1N4154 25PIV IR .1UA SI 6082-1012 14433 1N4154 CR 103 DIODE RECTIFIER IN645 6082-1016 14433 1N645 CR 105 DIODE 1K455 30PIV 1R 30UA GE 6092-1010 14433 1N455

Q 101 TRANSISTOR 2N3414 8210-1290 56289 2N3414 Q 102 TRANSISTOR 2N3414 8210-1290 56289 2N3414 Q 103 TRANSISTOR 2N3414 8210-1290 56289 2N3414 Q 104 TRANSISTOR 2N3414 8210-1290 56289 2N3414 Q 105 TRANSISTOR 2N1303 8210-1019 01295 2N1303 Q 106 TRANSISTOR 2N1303 8210-1019 01295 2N1303 Q 107 TRANSISTOR 2N3414 8210-1290 56289 2N3414 Q 108 TRANSISTOR 2N3414 8210-1290 56289 2N3414

R 101 RES COMP 100 K 5PCT 1/2W 6100-4105 81349 RCR20G104J R 102 RES COMP 470 K 5PCT 1/2W 6100-4475 81349 RCR20G474J R 103 RES FLM 6.98K 1 PCT l/2W 6450-1698 81349 RN65D6981F R 104 POT WW TRM 2K CHM 10 PCT 10T 6059-2209 80294 3067P-1-202

NOTE: Composition resistors may be replaced by the same value and power rating in 5% carbon film or 1% metal film.

MAINTENANCE 29 1538-A Strobotac

ELECTRICAL PARTS LIST (cont)

OSCILLATOR PC BOARD P/N 1538-2710 R 105 RES COMP 24 K OHM 5PCT l/4W 6099-3245 81349 RCR07G243J R 106 RES COMP 20 K OHM 5PCT 1/2W 6100-3205 61349 RCR20G203J R 107 RES COMP 2.4 K OHM 5PCT l/2W 6100-2245 81349 RCR20G242J R 108 RES FLM 14 K 1 PCT 1/2W 6450-2140 61349 RN6501402F R 109 RES COMP 2.2 K 5PCT 1/2W 6100-2225 81349 RCR20G222J R 110 RES COMP 4.7 K 5PCT l/2W 6100-2475 81349 RCR20G472J R 111 RES FLM 5.9 K 1 PCT 1/2W 6450-1590 81349 RN65D5901F R 112 RES COMP 620 OHM 5PCT 1/2W 6100-1625 81349 RCR20G621J R 113 RES FLM 5.49 K 1 PCT 1/2W 6450-l549 81349 RN65D5491F R 114 POT WW TRM 1K OHM 10 PCT 10T 6059-2105 80294 3067P-1-102 R 115 RES COMP 2.0 K OHM 5PCT 1/2W 6100-2205 81349 RCR20G202J R 116 RES COMP 10 K 5PCT 1/2W 6100-3105 81349 RCR20G103J R 117 RES COMP 1.0 K 5PCT 1/2W 6100-2105 81349 RCR20C102J R 118 RES COMP 1.0 K 5PCT 1/4W 6099-2105 81349 RCR07G102J R 120 RES COMP 43 K OHM 5PCT 1/2W 6100-3435 81349 RCR20G433J R 121 RES COMP 10 K 5PCT 1/2W 6130-3105 81349 RCR20G103J R 122 RES COMP 4.7 K 5PCT 1/2W 6100-2475 81349 RCR20G472J R 123 RES COMP 4.7 K 5PCT 1/4W 6099-2475 81349 RCR07G472J R 124 RES COMP 22 K 5PCT 1/4W 6099-3225 81349 RCR07G223J R 125 RES COMP 2.2 K 5PCT 1/4W 6099-2225 81349 RCR07G222J R 126 RES COMP 10 K 5PCT 1/2W 6100-3105 81349 RCR20G103J R 129 RES COMP 4.7 K 5PCT 1/2W 6100-2475 81349 RCR20G472J R 130 RES COMP 100 K 5PCT 1/2W 6100-4105 81349 RCR20G104J R 131 RES COMP 100 K 5PCI 1/2W 6100-4105 81349 RCR20G104J R 133 RES COMP 4.7 K 5PCT l/2W 6100-2475 81349 RCP20G472J R 134 RES COMP 22 K 5PCT 1/2W 6100-3225 81349 RCP20G223J

SWITCH CIRCUIT PC BOARD P/N 1538-2721 REFDES DESCRIPTION PART NO. FMC MFGR PART NO. C 201 CAP MYLAR 1.09 UF 1 PCT 100V 4860-8010 56269 410P 1.09 UF 1PCT C 202 CAP MYLAR 0.182 UF 1 PCT 100V 4860-7905 56289 410P 0.182 UF 1PCT C 203 CAP MYLAR 0.0301UF 1 PCT 100V 4860-7842 56289 410P 0.0301 UF 1PCT C 204 CAP MICA 4320 PF 1PCT 300V 4600-1350 72136 DM20FC4320PF1PCT4CR C 205 CAPACITOR 1531-4020 24655 1531-4020 C 206 CAPACITOR 1531-0470 24655 1531-0470 C 207 CAPACITOR 1538-0441 24655 1538-0441

R 201 POT COMP TRM 50 K OHM 20 PCT 15T 6001-3509 80294 3068P-1-503 R 202 RES COMP 24 K OHM 5PCT 1/2W D 6100-3245 81349 RCR20G243J R 203 POT COMP TRM 50K OHM 20 PCT 15T 6001-3509 80294 3068P-1-503 R 204 POT COMP TRM 50K OHM 20 PCT 15T 6001-3509 80294 3068P-1-503 R 205 RES COMP 10 K 5PCT 1/2W 6100-3105 81349 RCR20G103J R 206 RES COMP 4.7 K 5PCT 1/2W 6100-2475 81349 RCR20G472J R 207 RES FLM 464 K 1 PCT 1/2W 6450-3464 81349 RN65D4643F

30 MAINTENANCE 1538-A Strobotac

ELECTRICAL PARTS LIST (cont)

SWITCH CIRCUIT PC BOARD P/N 1538-2721 S 201 SWITCH ROTARY ASM 7890-3940 24655 7890-3940

PC BOARD ASM P/N 1538-2731 C 301 CAP ALUM 200-200 UF 50V 4450-5591 24655 4450-5591

CR 301 DIODE RECTIFIER 1N4003 6081-1001 14433 IN4003 CR 302 DIODE RECTIFIER IN4003 6081-1001 14433 IN4003 CR 303 DIODE RECTIFIER IN4003 6081-1001 14433 IN4003 CR 304 DIODE RECTIFIER IN4003 6081-1001 14433 IN4003 CR 305 DIODE RECTIFIER IN4003 6081-1001 14433 IN4003 CR 306 DIODE RECTIFIER 1N645 6082-1016 14433 1N645

Q 301 TRANSISTOR 2N1540 8210-1540 04713 2N1540 Q 302 TRANSISTOR 2N1303 8210-1019 01295 2N1303

R 301 RES COMP 1.0 K 5PCT 1/2W 6100-2105 81349 RCR20G102J R 302 RES COMP 1.8 K 5PCT 1/2W 6100-2165 81349 RCR20G182J R 303 RES COMP 47 K 5PCT 1/2W 6100-3475 81349 RCR20G473J R 304 RES WW MOLDED 3.0 OHM 10 PCT 2W 6760-9309 75042 8WH 3 OHM 10PCT

POWER SUPPLY PC BOARD P/N 1538-2751 C 501 CAP MYLAR 1.30UF 1 PCT 100V 4860-8285 56289 410P 1.30 UF 1PCT C 502 CAP PAPER .022UF 5PCT 600V U 4510-4001 56289 416P22356 C 503 CAP CER DISC 2200PF 10PCT 500V 4406-2228 72982 0871082Z5000222J C 504 CAP PAPER .022UF 10PCT 600V 4510-4000 56289 416P22396 C 505 CAP CER DISC 220PF 5PCT 500V 4404-1225 72982 0831082Z5D00221J C 506 CAP CER DISC 1000PF 5PCT 500V 4405-2105 72982 0801082Z5D00102J C 509 CAP ALUM 600-300-300 UF 75V 4450-5606 56289 60D 75V C 511 CAP CER SQ 0.01UF 80/20PCT 100V 4403-4100 72982 8131M100651104Z

POWER SUPPLY PC BOARD P/N 1538-2751 REFDES DESCRIPTION PART NO. FMC MFGR PART NO. CR 501 DIODE RECTIFIER 1N645 6082-1016 14433 1N645 CR 502 DIODE 1N4154 25P1V IR.1UA SI 6082-1012 14433 1N4154 CR 503 DIODE RECTIFIER 1N4003 6081-1001 14433 1N4003 CR 504 ZENER DIODE 37V 1PCT 1W 6083-1110 24655 6083-1110 CR 505 DIODE RECTIFIER 1N645 6082-1016 14433 1N645 CR 507 RECT MV16A 1600P1V 50MA SI A3H 6081-1015 13327 MV1LA CR 508 DIODE RECTIFIER 1N4003 6081-1001 14433 1N4003 CR 509 DIODE RECTIFIER 1N4003 6081-1001 14433 1N4003 CR 510 DIODE RECTIFIER 1N4003 6081-1001 14433 1N4003 CR 511 DIODE RECTIFIER 1N4003 6081-1001 14433 1N4003 CR 516 ZENER 1N965B 15V 5PCT .4W 6083-1015 14433 1N9658 CR 517 ZENER 1N748A 3.9V 5PCT .4W 6083-1002 14433 1N748A

L 501 CHOKE MOLDED 1.8 UH 10PCT 4300-1100 99800 1537-18

MAINTENANCE 31 1538-A Strobotac

ELECTRICAL PARTS LIST (cont)

POWER SUPPLY PC BOARD P/N 1538-2751 REFDES DESCRIPTION PART NO. FMC MFGR PART NO. Q 501 TRANSISTOR 2N1305 8210-1305 01295 2N1305 Q 502 TRANSISTOR 2N3414 8210-1290 56289 2N3414 Q 503 TRANSISTOR 2N3414 8210-1290 56289 2N3414 Q 504 TRANSISTOR 2N3414 8210-1290 56289 2N3414 Q 506 TRANSISTOR 2N697 8210-1040 04713 2N697 Q 507 TRANSISTOR 2N3414 8210-1290 56289 2N3414 Q 508 TRANSISTOR 2N697 8210-1040 04713 2N697 Q 509 TRANSISTOR 2N1305 8210-1305 01295 2N1305 Q 510 TRANSISTOR 2N1546 8210-1073 04713 2N1546

R 501 RES COMP 47 K 5PCT 1/2W 6100-3475 81349 RCR20G473J R 502 RES COMP 3.3K 5PCT 1/2W 6100-2335 81349 RCR20G332J R 503 RES COMP 91 OHM 5PCT 1/2W 6100-0915 81349 RCR20G910J R 504 RES WW AX LEAD 82 OHM 5 PCT 3W 6680-0825 75042 AS-2 82 OHM 5PCT R 505 RES COMP 47 OHM 5PCT 1/21W 6100-0475 81349 RCR20G470J R 506 RES COMP 1.0 K 5PCT 1/2W 6100-2105 81349 RCR20G102J R 507 RES COMP 2.2 K 5PCT 1/2W 6100-2225 81349 RCR20G222J R 508 RES FLM 34 K 1 PCT 1/2W 6450-2340 81349 RN6503402F R 509 RES COMP 2.2 K 5PCT 1/2W 6100-2225 81349 RCR20G222J R 510 RES COMP 1.0 K 5PCT 1/2W 6100-2105 81349 RCR20G102J R 512 RES COMP 47 K 5PCT 1/2W 6100-3475 81349 RCR20G473J R 513 RES COMP 10 K 5PCT 1/2W 6100-3105 81349 RCR20G103J R 514 RES COMP 47 K 5PCT 1/2k 6100-3475 81349 RCR20G473J R 515 RES COMP 22 K 5PCT 1/2W 6100-3225 81349 RCR20G223J R 518 RES COMP 18 K 5PCT 1/2W 6100-3185 81349 RCR20G183J R 519 RES COMP 18 K 5PCT 1/2W 6100-3185 81349 RCR20G183J R 520 RES COMP 1.0 K 5PCT 1/2W 6120-2105 61349 RCR42G102J R 521 RES COMP 27 OHM 5PCT 1/2W 6100-0275 81349 RCR20G270J R 522 RES COMP 620 K OHM 5PCT 1/2W 6100-4625 81349 RCR20G624J R 523 RES COMP 10 K 5PCT 1/2W 6100-3105 81349 RCR20G103J R 525 RES COMP 27 K 5PCT 1/2W 6100-3275 81349 RCR206273J R 526 RES COMP 3.3 K 5PCT 1/2W 6100-2335 81349 RCR20G332J R 529 RES COMP 270 OHM 5PCT 1/2W 6100-1275 81349 RCR20G271J

T 501 TRANSFORMER POWER 0345-4130 24655 0345-4130 T 502 TRANSFORMER INDUCTOR 0746-4450 24655 0746-4450

32 MAINTENANCE 1538-A Strobotac

NOTE; The number appearing on the foil side is not Type 1538-P4 High-Intensity-Flash Capacitor the part number. The dot on the foil at the transistor (See Figure 2-14) socket indicates the collector lead. With the Type 1538-P4 High-Intensity-Flash Capaci- tor connected to the Type 1538 (refer to paragraph 2.11.7), it is possible to produce a single brilliant flash of 44 million beam candles with an 8-ms duration. This accessory should be used when the object being photographed is operating at extremely high speed or in unavoidably high ambient light.

Some of the many accessory instruments available Type 1538-P2 Extension Lamp for use with the stroboscopes. The Type 1538-P2 Extension Lamp consists of a lamp- and-reflector assembly identical to that on the Strobotac, with a six-foot cord and plug. This light- weight lamp assembly makes a convenient accessory for observing the motion of object; in those hard-to- reach places.

The reflector is identical to that of the 1538 Strobotac. The entire assembly (excluding the connecting cable) is 7 inches (180 mm) long; its weight, (including the cord) is 8 ounces (0.3 kg). Custom cables of any length can be ordered.

MAINTENANCE 33 1538-A Strobotac

APPENDIX

Type 1539-A Stroboslave Power Required: 100 to 125 or 195 to 250 V, 50 to 400 c/s, 16 W. The Type 1539 Stroboslave is an auxiliary light-source Accessories Supplied: Phone plug for input. that will produce a flashing light with output charac- Accessories Available: Type 1537-A Photoelectric teristics that are similar to the Type 1531 Strobotac. Pickoff, Type 1531-P2 Flash Delay This compact stroboscope will flash on command (with a Type 1536-A Photoelectric Pickoff). when triggered from a contact closure or from a va- riety of equipment including the Type 1531 or the Type Mechanical Data: 1538 Strobotacs. Net Shipping Width Height Depth Weight Weight

imn mnimmnimmblgkblgk

24½ 68853/ 281 451/ 140 233/ 187. 3.

Type 1531-P2 Flash Delay

The Type 1531-P2 Flash Delay provides a continuously adjustable time-delay between an external triggering device and a Stroboscope. The triggering de- SPECIFICATIONS vice can be an oscillator, photocell or other type of transducer. Flashing-Rate Ranges: 0 to 700, 0 to 400, 0 to A typical combination of flash delay, photoelectric 25,000 flashes per min on high-, medium-, and low- pickoff and stroboscope can be used for visual ob- intensity ranges, respectively. servation and analysis of repetitive motion whose Flash Duration: Approx 0.8, 1.2, and 3ms, measured period is not constant. The flash delay also provides at 1/3 peak intensity, for the low-, medium-, and high- means for precise synchronization of camera shutter, intensity ranges, respectively. stroboscopic flash, and objects moving at irregular Peak Light Intensity: Typically 0.6, 3.5, and 11 speeds, for high-speed photography or other purposes. million beam candles (0.6, 3.5, and 11 X 106 lux measured at 1-m distance at the beam center), for low-, medium-, and high-intensity ranges, respectively. For single flash, 18 million beam candles at 1 meter. Reflector Beam Angle: 10° at half-intensity points. External Triggering: Either a switch closure across the input jack terminals or a 2-V (peak) positive pulse.

34 Appendix 1538-A Strobotac

SPECIFICATIONS

SPECIFICATIONS Maximum Pulse Rate: Approximately 2500 pulses/ s as limited by the 200-µs time constant of the photo- Time-Delay Range: Approximately 100 ms to 0.8 cell and cable combination. ms in three ranges. Power Required: 20 to 28 V dc, 40 mA. Power is Output Pulse: >13 V available for triggering the Type supplied by the Type 1531-P2 Flash Delay or the Type 1531-A and 1538-A Strobotac® electronic strobo- 1150-B (or Type 1151-A) Digital Frequency Meter. scopes and the Type 1539-A Stroboslave. Accessories Supplied: 10-ft roll of 3/8-in black tape; Sensitivity: As little as 0.3V input will produce suf- 10-ft roll of 3/8-in silver tape; carrying case. ficient output to trigger the stroboscope. Mounting: C-clamp (capacity 1 5/16 in, flat or round) Input: Phone jack for triggering; jack for camera or 1 ½-in magnet, both supplied. Net Weight: 1¼ lb synchronization. (0.6 kg). Accessories Available: Type 1536-A Photoelectric Shipping Weight: 4 lb (1.9 kg). Pickoff. Power Required: 105 to 125 or 210 to 250 V, 50 to 400 c/s, 5 W with Type 1536-A connected. Type 1537-A PHOTOELECTRIC PICKOFF Mechanical Data: In appearance, the Type 1537 Photoelectric Pickoff Net Shipping is similar to the Type 1536. The Type 1537, however, Width Height Depth Weight Weight has no light source; the photosensitive element is a imn mnimmnimmblgkblgk silicon light-activated switch. The output from this transducer will directly trigger the Type 1538 551/8 183 301/ 84363/ 921532. Strobotac or the Type 1539 Stroboslave.

SPECIFICATIONS

Type 1536-A Photoelectric Pickoff Operating Rate: Greater than 2500 pulses/s. Power Required: 3 to 25 V dc; 0 to 100 mA de- The Type 1536 Photoelectric Pickoff contains a light pending on operating rate. Power is supplied by in- source, an optical system and a photocell that pro- strument with which it is used. duces a pulse when light from a moving object is re- Accessories Supplied: 10-ft roll of 3/8-in black tape, flected back to the photocell. This output pulse is fed 10-ft roll of 3/8-in silver tape, carrying case. through a Type 1531-P2 Flash Delay, and then used Mounting: C-clamp (capacity 1 5/16 in, flat or round) to trigger a Stroboscope. With this combination of in- or 1½-in magnet, both supplied. struments, the motion of objects rotating at irregular Net Weight: 1½ lb (0.7 kg). speeds can be analyzed visually or by photographic Shipping Weight: 4½ lb (2.1 kg). means.

Appendix 35